The TCP 3-Way Handshake: How the Internet Says ‘Hello’

Every time you visit a website, your computer and the server start a little conversation to ensure a smooth and reliable connection. This conversation is called the TCP 3-Way Handshake — and it's the backbone of how reliable data travels across the internet.

---

What is TCP?

TCP (Transmission Control Protocol) is one of the main protocols in the internet protocol suite. It's designed to provide reliable, ordered, and error-checked delivery of data between applications.

---

What is the TCP 3-Way Handshake?

It's the initial setup process between a client and server before any data is exchanged. Think of it as a polite “hello” followed by a firm “we’re ready” from both sides.

The 3 Steps:

1. SYN (Synchronize)
   Client sends a message to the server saying:
   “Hey, I want to start a conversation. Here's my sequence number!”

2. SYN-ACK (Synchronize-Acknowledge)
   Server replies:
   “Got your message! Here's my own sequence number and I'm acknowledging yours.”

3. ACK (Acknowledge)
   Client responds:
   “Cool, let’s begin.”
   Now the connection is established, and data transfer can begin!

---

Sequence Numbers and ACKs

• Each device sends a sequence number to track the data sent.

• ACKs (Acknowledgments) confirm which packets were received.

• If something is lost, TCP resends it — this makes TCP reliable (unlike UDP, which just sends and forgets).

---

Why It Matters

• Ensures both devices are ready and synchronized before sending data

• Enables reliable and ordered delivery

• Prevents loss and duplication of data

• Forms the foundation of secure communication like HTTPS

---

TCP vs UDP (Quick Comparison)

---